This invention relates to polyvinyl chloride ("PVC") foam made with physical blowing agents, more particularly to PVC foam blown with one or more gaseous hydrofluorocarbons ("HFC"s) such as HFC-134a (1,1,1, 2-tetrafluoroethane).
There are publications (such as "Inert-Gas Extrusion of Rigid PVC Foam" by S. K. Dey et al in the Journal of Vinyl & Additive Technology, March 1996, Vol. 2, No. 1) disclosing the use of inert gaseous blowing agents (such as CO.sub.2) and chemical blowing agents (such as azodicarbonamide) for making PVC foams. Chemical blowing agents present disadvantages such as the leaving of residues in the foam and inflexible processing since the blowing agent is water sensitive and usually must be premixed with the PVC. Inert blowing agents such as CO.sub.2 tend to restrict the ability to vary the foam density, generally resulting in high density foams. What is desired is a blowing agent which provides processing flexibility and the ability to achieve a range of densities.